After World War I, France was concerned about Germany becoming militarized again and invading France. In an attempt to preempt this, France developed a protective barrier along the German and Swiss borders. The Maginot Line was built between 1929 and 1938 with some of the best military technology of the time and seemed impenetrable. Unfortunately for the French, they decided not to build the Maginot Line at full strength by the Belgian border, as Belgium was a country that remained neutral, and France did not want to do anything that could bring conflict into Belgium. The Germans realized this and invaded France through Belgium, rendering the Maginot Line useless to stop an outside invasion. While the Line initially seemed like a deterrent to invasion, the decision not to fortify it fully was what ultimately lead to France’s downfall in World War II.

The War of the Spanish Succession began in 1701 over who would rule over the Spanish Empire after the death of Charles II. The empire that the Habsburgs had built up extended all over Europe and was of great interest to many European leaders. After some attempts to achieve a practical solution, Charles II declared that Philip, Duke of Anjou, a grandson of the King of France, would become the next emperor. This would have given France a tremendous amount of power, and this worried many countries, particularly England, the Netherlands, and Austria, who worked to counteract this expansion of French power. The ensuing conflicts lasted until 1714, when a variety of treaties, collectively called the Peace of Utrecht, were reached that broke down to most of the empire being divided up among the European powers and Philip ruling Spain after agreeing not to seek the French crown.

Following the end of World War I, much of Europe lay in ruins, and most of the European governments did not have the money or the resources to rebuild. The United States realized that it needed to take a lead in rebuilding Europe, not only to help the countries, but also to lower the chances that communism would take hold in Western European countries. Some of the Eastern European countries had already succumbed to communism, and the USSR was in a position to expand its influence. The plan was named after the Secretary of State, George Marshall, and was implemented in 1948 with support from Congress and President Truman. The plan, which spent billions of dollars helping to rebuild Europe and its economy, was quite successful and is credited with helping Europe to recover. It also showed the disadvantages of communism when the USSR refused American aid to help East Germany and other countries within the Soviet Bloc.

The War of the Austrian Succession began in 1740 when Frederick the Great invaded Austria-controlled Silesia under the pretense of Maria Theresa not being a lawful heir to the Austrian throne, which she obtained following the death of her father Charles VI in that same year.

When France ceded Canada to Britain in 1763, the colonists living there became British subjects. The Quebec Act of 1774 was meant to appease them and win over their loyalty to Britain, not deport them from the country. The incredibly sparse colonial population of Canada at the time necessitated measures to keep subjects in Canada, not expel them.

The Thirty Years' War occurred in the 17th century, lasting from 1618 to 1648. The other three conflicts spanned the 18th century: War of the Spanish Succession (1701-1714), War of the Austrian Succession (1740-1748), and Seven Years' War (1754-1763).

Klemens von Metternich lived over a century after the close of the Thirty Year's War, and is best known as being the Foreign Minister of the Austrian Empire and presiding over the Congress of Vienna. The Peace of Westphalia was the treaty that ended the Thirty Years' War. The Battle of White Mountain was a significant conflict in the early part of the war. Albrecht von Wallenstein was a prominent mercenary leader during the war. Gustavus Adolphus was the king of Sweden who intervened on behalf of the Protestant cause.

The Italians provided forces in excess of 50,000 land troops, and the Nazi regime tested bombing strategies and technologies during the war, as famously depicted in Picasso’s Guernica. Tens of thousands of foreign volunteers fought in the International Brigades, and Spanish anarchists resisted the fascist and conservative forces. The French Popular Front government of Leon Blum was officially neutral.

The Treaty of Brest-Livotsk was signed between the newly formed Bolshevik government of the Soviet Federated Socialist Republic (the USSR) and the Central Powers, granting the Baltic States to Germany and the Kars Oblast to the Ottomans, while also paying the Germans massive reparations. Germany’s defeat and acceptance of the Treaty of Versailles negated Brest-Livotsk. The first Battle of the Somme was an inconclusive but bloody engagement between Britain, France and Germany in Western Europe in 1916. The Battle of Tannenberg was a decisive defeat of the Russians by the German General von Hindenburg at the beginning of World War I. The Spring Offensive of 1918 was a series of advances by Germany in Western Europe using storm troopers that were ultimately reversed by American reinforcements.

When Archduke Franz Ferdinand of Austria was assassinated by Serbian radicals, Austria-Hungary declared war on Serbia. Unbeknownst to Austria, Serbia had signed a secret treaty with Russia, who had signed a secret treaty with France, who had signed a secret treaty with Britain. Austria, who had signed a secret treaty with Germany and the Ottoman Empire, prepared for war with Serbia, only to discover that it would be fighting half of Europe to do so. The diplomatic catastrophe became known as the July Crisis, as war with all European countries involved took less than a month to begin after Ferdinand's assassination June 28th 1914.